Bump again. On Fri, Mar 1, 2019 at 2:31 PM Gabe Black <gabebl...@google.com> wrote:
> Bump... > > On Wed, Feb 27, 2019 at 9:13 PM Gabe Black <gabebl...@google.com> wrote: > >> Hi folks. TLM is a communication protocol/mechanism built on top of >> systemc. It supports a mechanism called DMI which stands for direct memory >> interface. The idea is that an entity sending a request into the system can >> ask if the target can give it a pointer it can use to directly access that >> memory in the future. The target, if it supports that sort of thing, >> returns a descriptor which describes a region of memory that can be >> accessed in that way. If that needs to be invalidated in the future, then >> there's another mechanism the target can use to communicate back to the >> sender telling it to throw away that descriptor. >> >> The way this mechanism is implemented in TLM is a bit less than ideal >> since every request has a field that says whether the requester wants to >> know about DMI, and so the target has to perform an extra check on all the >> requests in case someone is asking when that's useful to communicate only a >> very small fraction of the time, perhaps only once during an entire >> simulation. >> >> Aside from that though, this mechanism has some nice properties. First, >> it avoids having to globally identify what a memory is or where it is for a >> particular simulation. A memory is just a thing on the other end of a >> request that may let you get at it directly if you ask nicely. Also, if >> there's something in the way that would get messed up if you skipped over >> it, say a cache, it can block those requests from getting through to >> targets. This could be useful for KVM for instance, when it's collecting >> regions to act as RAM for the virtual machine. >> >> I haven't fully figured out what a good way to avoid the check-every-time >> problem of the systemc mechanism, and ideally whatever I/we come up with >> will be compatible enough to be bridged effectively, but I'm thinking some >> sort of explicit additional call like getAddrRanges which would propogate >> through the hierarchy at specific points, either to a specific address or >> as a broadcast. >> >> I know some folks have looked at gem5's memory system protocol and >> systemc's TLM before, for instance either to try making gem5 use TLM >> natively, or for the systemc TLM bridges. What do you think about adding >> this sort of mechainsm to gem5? Are there any pitfalls to avoid, known >> issues to figure out, suggested avenues to explore, etc? Please let me >> know. This is likely something I'm going to want to pursue in the next few >> weeks. >> >> Gabe >> > _______________________________________________ gem5-dev mailing list gem5-dev@gem5.org http://m5sim.org/mailman/listinfo/gem5-dev
